1. Field of the Invention
The invention relates to electric motor power systems, in particular to an electronic system for either an alternating current (hereinafter AC) type motor or an induction-type motor, such as a motor using a permanently split capacitor (hereinafter PSC), or a shaded pole type of an AC induction motor.
2. Discussion of the Prior Art
The general concept of charging a capacitor through a diode while the motor is turned ON so that the charge on the capacitor may be applied across the motor to provide a force when the motor is turned OFF is well known in the prior art related to systems for AC-type motors. There are several examples of this general concept in the patent literature.
U.S. Pat. No. 2,929,977 to Choudhury discloses a dynamic system for induction motors. The system utilizes a capacitor charged by connection to an AC power source through a rectifier which for the capacitor is connected between two phase terminals of the motor in order to supply direct current excitation of two terminals between which the primary winding is not connected after a sufficient time delay for the motor speed to be reduced by the effect of the capacitor.
U.S. Pat. No. 3,341,758 to Plumpe, Jr. discloses a motor system using a signal-controlled rectifier (SCR) which is fired to discharge a direct current (hereinafter DC) potential across a capacitor through an AC motor winding. A second capacitor is charged to a DC potential to maintain the SCR nonconductive until the AC source voltage to the motor has been interrupted.
U.S. Pat. No. 3,475,669 to Oltendorf discloses a variable dynamic DC brake for an AC motor wherein a relatively large brake storage capacitor is connected in a charging circuit connected to an AC power supply for the motor. The charging circuit provides means to adjust the maximum charge on the brake capacitor and includes a signal-controlled rectifier (SCR) connected in series with the brake capacitor.
U.S. Pat. No. 4,095,151 to Mourick discloses an arrangement for an AC series motor with a switching device for changing from a running motor to an operation having a series circuit consisting of a capacitor and a charging diode associated therewith. To avoid an additional resistor for limiting the capacitor charging current, the capacitor and charging diode are connected such that the armature winding is shunted by the series circuit consisting of the capacitor and the charging diode. A switch contact is connected between the center of the series connection and the external terminal of the field winding so that, during motor operation, a series circuit consisting of the capacitor, the charging diode and the field winding is connected between the terminals of the AC series motor. In operation, the armature winding in series with the field winding is shunted by the capacitor which has a potential that provides a braking force. However, this universal motor is not applicable to the present invention.
U.S. Pat. No. 4,195,255 to Guttmann discloses an electronic brake for AC motors. A controlled rectifier applies a direct current to the motor and a control turns the rectifier on for a timed interval determined by the charging rate of a timing capacitor through a variable resistance after deactivation of the motor.
U.S. Pat. No. 4,374,352 to Webster discloses an AC induction motor system. A three-terminal network, which electrically senses the time the voltage is applied to an AC induction motor, is removed and concurrently therewith utilizes energy previously stored in a capacitor to effect an eddy current in the motor. However, this AC induction motor with its complicated circuitry is not applicable to the present invention.
U.S. Pat. No. 4,450,397 to Painter et al. discloses an electronic AC induction motor control circuit including a selectively signal-controlled rectifier (SCR) which operates in a first conductive mode to apply a rectified current to a winding to brake the motor and in a second nonconductive mode. A switching circuit coupled to the rectifier is responsive to the disconnecting of the AC voltage source from the winding for switching the rectifier between the first and second modes of operation at a second switching rate different from a first switching rate to brake the motor at a corresponding second rate.
U.S. Pat. No. 5,705,903 to Hastings discloses an electric brake for an AC motor designed for bringing the motor to a rapid halt. The electric brake includes a capacitor C1 which is charged to a preselected voltage when the motor is ON. A shunt regulator 18 prevents the capacitor from overcharging by shunting the charging current to ground after the capacitor reaches the preselected voltage. However, this universal motor is not applicable to the present invention.
Japanese Patent No. 58-124685 to Aoki discloses a method for stopping a motor utilizing three switches S1, S2, S3, capacitors C1 and C2, and a diode D which is used to charge capacitor C2, such that, when switch S2 is closed, the discharging of the charge accumulated in the capacitor C2 through the motor provides a braking force. See FIG. 2.
Japanese Patent No. 5-064474 to Miyama et al. discloses a brake system for an AC motor wherein an AC voltage commercial power supply is stepped down through a step-down transformer and rectified through a rectifier, such that the rectified output passes through capacitors 17 and 15 to produce a smoothed DC voltage. At the same time, the capacitor 15 is charged through a resistor 13. This patent gives basic information and provides common knowledge about an AC motor using DC voltage for a brake. The patentees are using AC induction, not a shaded pole, and a synchronous motor. They admit that this circuit may not be able to stop the motor. Therefore, an outside braking source may be required. This Japanese circuit is using a signal-controlled rectifier (SCR) that is controlled through a voltage regulator which is a monostable multivibrator circuit MM 19, clamped by a Zener diode 53. This prior art circuit is also using two switches 5 and 37 and a full wave bridge comprised of diodes 47 and 49. Because Miyama et al. are controlling the charging voltage as well as the rate of discharge, the AC motor cannot stop quickly.
Based upon a preliminary review, the patents to Mourick, Webster, Hastings and Aoki appear to disclose the general concept of a system for an AC-type motor wherein a capacitor is charged through a diode and/or resistor during run mode operation, and the DC voltage stored in the capacitor is dropped across the coil of an AC motor during an OFF or STOP mode operation to provide a dynamic force. Other references discussed above relate more to the evolution and/or state-of-the-art in regard to systems for AC-type motors in general.
Despite developments in the prior art, no simple circuitry comprised of a capacitive element, an AC voltage rectifying diode, an electrolytic capacitor, a pair of resistive elements which control the charge rate of the capacitive element, and a relay or switch for controllably transferring the operation of a motor to and from a run mode operation, i.e. an ON mode operation, and a braking mode operation, i.e. a STOP or OFF mode operation, has been developed.